1. Field of the Invention
The present invention relates to a camera having a zoom optical system. More particularly, this invention is concerned with a camera having a zoom optical system in which when picture sizes are switched, a ratio of a subject size to a picture size Is automatically held unchanged.
2. Related Background Art
As already known, a camera having a zoom optical system and using a roll film of 35 mm wide has been made available in recent years. In this camera, the picture size can be selectively switched between, for example, a normal full size (hereafter, normal size) of 36 mm by 24 mm that is called a Leica size and a size of 36 mm by 13 mm (hereafter, panoramic size) whose vertical dimension is smaller than the normal size.
When the picture size Is variable, a ratio of a subject size to a selected picture size must remain unchanged. To cope with this matter, Japanese Laid-Open Patent Application No. 62-251729 or Japanese Laid-Open Patent Application No. 63-220118 has proposed a camera including an auto zoom function in which a photographer can pre-set a ratio of a portrait size to a picture frame.
Japanese Laid-open Patent Application No. 2-20834 has disclosed a motor-driven zoom camera in which the longitudinal and lateral positions of the camera during photography are detected so that the image magnification for the auto zoom mode will be variable. Using this motor-driven zoom camera, a photographer need not be concerned about zooming but need merely follow a subject. This results in photographs in each of which a ratio of a subject size to a picture frame; that is, a magnification for imaging a subject on film is set to an intended value.
However, in a camera art that makes it possible to automatically set a ratio of a subject size to a picture frame to an intended value and is disclosed in the above Japanese Laid-open Patent Application No. 2-20834, the picture frame is fixed. Therefore, if the camera permits selection of the aforesaid normal mode or panoramic mode, the problems below arise.
Specifically, as shown in FIG. 11, even when a magnification for imaging a subject 41 on a film 43 is set to an intended value, if the normal mode is switched to the panoramic mode, the vertical length of the picture frame becomes smaller. Therefore, using the same imaging magnification value, as shown in FIG. 12, the top and bottom of the subject 41 are cut out. To produce a full-length portrait 42 of the subject in panoramic mode, as shown in FIG. 13, the imaging magnification must be set to a small value.